It is increasingly important that a physician or surgeon delivering substances, such as drugs, is able to efficiently and accurately locate the desired target tissue for effective delivery of the substance. This is particularly true when the concentration of the substance required at the target site cannot be safely or effectively achieved by introduction of the substance to a location remote from the target site. Currently, it is difficult to determine injection depth and/or tissue type without visually guiding the needle of an injection device or having some other indication of the needle location within a patient's body.
For example, fluoroscopy can be used to guide the injection device, but fluoroscopy lacks the resolution and sensitivity needed to accurately guide the injection device into the desired tissue location. Alternatively, electrocardiograph signals have been used when delivering substances to ventricular tissues of the heart, but this technique cannot be used throughout the entire body. In addition, the use of imaging systems (e.g., ultrasonic, magnetic resonance, and optical) to view the injection device and surrounding tissue has been proposed, but the barriers to usage of such systems are large (e.g., including large capital investment, large space requirements, and ownership of intellectual property by others).